DOCSLIB.ORG

Wide Angle Perspective

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Wide Angle Perspective Being familiar with 35mm traditional film and digital photography, this at least for me is a good starting point to wrap my head around what we refer to as “Wide-field Astrophotography.” In traditional photography, on a full frame 35mm camera, a lens is generally considered to be "wide angle" when its focal length is less than around 35mm. This translates into an angle of view which is greater than about 55° across your photo's widest dimension. The definition of ultra-wide is a little fuzzier, but most agree that this realm begins with focal lengths somewhere around 20-24 mm and less. Regardless, the key concept is this: the shorter the focal length, the more you will tend to notice the unique effects of a wide angle lens. The above diagrams depict the maximum angles that light rays can take when hitting your camera's sensor. The location where light rays cross is not necessarily equal to the focal length, but is instead roughly proportional to this distance. The angle of view therefore still increases similarly. What makes a wide angle lens unique? A common misconception is that wide-angle lenses are primarily used for when you cannot step far enough away from your subject, but yet still want to capture all of this subject in a single camera frame. Unfortunately, if one were to only use it this way they'd really be missing out. In fact, wide angle lenses are often used for just the opposite: when you want to get closer to a subject! So, let's take a closer look at just what makes a wide angle lens unique: Its image encompasses a wide angle of view It generally has a close minimum focusing distance Although the above characteristics might seem pretty basic, they result in a surprising range of possibilities. The rest of this page focuses on techniques for how to best use these traits for maximal impact in wide angle photography. WIDE ANGLE PERSPECTIVE Obviously, a wide angle lens is special because it has a wide angle of view — but what does this actually do? A wide angle of view means that both the relative size and distance is exaggerated when comparing near and far objects. This causes nearby objects to appear gigantic, and far away objects to appear unusually tiny and distant. The reason for this is the angle of view: Wide Angle Lens Telephoto Lens (objects are very different sizes) (objects are similar in size) Even though the two cylinders above are the same distance apart when photographed with each lens, their relative sizes are very different when one fills the frame with the closest cylinder. With a wider angle of view, further objects therefore comprise a much lower fraction of the total angle of view. A misconception is that a wide angle lens affects perspective, but strictly speaking, this isn't true. Perspective is only influenced by where you are located when you take a photograph. However, in practical use, wide-angle lenses often cause you to move much closer to your subject — which does affect perspective. WIDE ANGLE PERSPECTIVE vs. TELEPHOTO A lens is generally considered to be "medium telephoto" when its focal length is greater than around 70 mm. However, many don't consider a lens a "full telephoto" lens until its focal length becomes greater than around 135 mm. This translates into an angle of view which is less than about 15° across your photo's widest dimension. A common misconception is that telephoto lenses are just for capturing distant objects. While this is a legitimate use, there's a whole array of other possibilities, and often time’s distant objects are better photographed by simply getting a little closer. Yes, this isn't practical with a lion, or a deep sky faint-fuzzy object but a pet or a person will likely appear better when they aren't photographed from afar. Why? The distance from your subject actually changes your photo's perspective, even if your subject is still captured at the same size in your camera frame. A narrow angle of view means that both the relative size and distance is normalized when comparing near and far objects. This causes nearby objects to appear similar in size compared to far away objects — even if the closer object would actually appear larger in person. The reason for this is the angle of view. So what does that mean? A telephoto lens not only magnifies the subject, but it also tends to compress perspective and provides a sufficiently narrow angle of view to Isolate the subject. The perspective compression characteristic of a telephoto lens makes distant background objects appear closer to your subject and in a more similar scale. Simply put, a telephoto lens "brings subjects closer", while a wide angle lens seems to make subjects appear further away than they actually are. The result is a compressed and expanded perspective, respectively.” This focal length comparison animation located at Canon USA’s website helps to demonstrate how the focal length of a lens affects angle of view: (http://www.usa.canon.com/app/html/EFLenses101/focal_length.html ) So what does all this have to do with astrophotography? If you recall, some of you rather than invest in complicated and expensive gear got your start in astrophotography via 35mm film of a DSLR and the lenses which were often used for this purpose fell within the 28 – 300mm focal length range. However, quality optics of your typical fixed focal length prime lenses in the 300-800mm range, carry hefty price tags starting around $1200 for a f/4.0 300mm to more than $13K; the other issue related to DSLR astrophotography are HEAT and NOISE. These considerations do not preclude one from engaging solely in DSLR astrophotography. ENTER THE TELESCOPE, ASTROGRAPHS AND THE LIKE OK, so we’ve come full-circle – sort of. When one is considering Wide-field astrophotography with CCD cameras, the level of complexity therein increases. This brings us back to telescope optics and pixel size. The best source of information IMHO related to this topic which attempts to simplify the concepts of Wide-field astrophotography with CCD cameras, is Apogee Imaging Systems CCD University: http://www.ccd.com/ccdu.html While this is certainly not an exhaustive source, it does help to put into perspective what we tend to discuss as Wide-field astrophotography in its simplest form. The complexity at least to me does not reside with DSLR based astrophotography. It rears its ugly head when one introduces CCD cameras and the major issues one is confronted when attempting to match a particular scopes focal length and optics, choice of imaging planetary or deep space objects and ones seeing conditions for any given site when choosing a CCD camera. .
Load more

Recommended publications
  • Noise and ISO CS 178, Spring 2014
    Noise and ISO CS 178, Spring 2014 Marc Levoy Computer Science Department Stanford University Outline ✦ examples of camera sensor noise • don’t confuse it with JPEG compression artifacts ✦ probability, mean, variance, signal-to-noise ratio (SNR) ✦ laundry list of noise sources • photon shot noise, dark current, hot pixels, fixed pattern noise, read noise ✦ SNR (again), dynamic range (DR), bits per pixel ✦ ISO ✦ denoising • by aligning and averaging multiple shots • by image processing will be covered in a later lecture 2 © Marc Levoy Nokia N95 cell phone at dusk • 8×8 blocks are JPEG compression • unwanted sinusoidal patterns within each block are JPEG’s attempt to compress noisy pixels 3 © Marc Levoy Canon 5D II at dusk • ISO 6400 • f/4.0 • 1/13 sec • RAW w/o denoising 4 © Marc Levoy Canon 5D II at dusk • ISO 6400 • f/4.0 • 1/13 sec • RAW w/o denoising 5 © Marc Levoy Canon 5D II at dusk • ISO 6400 • f/4.0 • 1/13 sec 6 © Marc Levoy Photon shot noise ✦ the number of photons arriving during an exposure varies from exposure to exposure and from pixel to pixel, even if the scene is completely uniform ✦ this number is governed by the Poisson distribution 7 © Marc Levoy Poisson distribution ✦ expresses the probability that a certain number of events will occur during an interval of time ✦ applicable to events that occur • with a known average rate, and • independently of the time since the last event ✦ if on average λ events occur in an interval of time, the probability p that k events occur instead is λ ke−λ p(k;λ) = probability k! density function 8 © Marc Levoy Mean and variance ✦ the mean of a probability density function p(x) is µ = ∫ x p(x)dx ✦ the variance of a probability density function p(x) is σ 2 = ∫ (x − µ)2 p(x)dx ✦ the mean and variance of the Poisson distribution are µ = λ σ 2 = λ ✦ the standard deviation is σ = λ Deviation grows slower than the average.
    [Show full text]
  • Estimation and Correction of the Distortion in Forensic Image Due to Rotation of the Photo Camera
    Master Thesis Electrical Engineering February 2018 Master Thesis Electrical Engineering with emphasis on Signal Processing February 2018 Estimation and Correction of the Distortion in Forensic Image due to Rotation of the Photo Camera Sathwika Bavikadi Venkata Bharath Botta Department of Applied Signal Processing Blekinge Institute of Technology SE–371 79 Karlskrona, Sweden This thesis is submitted to the Department of Applied Signal Processing at Blekinge Institute of Technology in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering with Emphasis on Signal Processing. Contact Information: Author(s): Sathwika Bavikadi E-mail: [email protected] Venkata Bharath Botta E-mail: [email protected] Supervisor: Irina Gertsovich University Examiner: Dr. Sven Johansson Department of Applied Signal Processing Internet : www.bth.se Blekinge Institute of Technology Phone : +46 455 38 50 00 SE–371 79 Karlskrona, Sweden Fax : +46 455 38 50 57 Abstract Images, unlike text, represent an effective and natural communica- tion media for humans, due to their immediacy and the easy way to understand the image content. Shape recognition and pattern recog- nition are one of the most important tasks in the image processing. Crime scene photographs should always be in focus and there should be always be a ruler be present, this will allow the investigators the ability to resize the image to accurately reconstruct the scene. There- fore, the camera must be on a grounded platform such as tripod. Due to the rotation of the camera around the camera center there exist the distortion in the image which must be minimized.
    [Show full text]
  • Making Your Own Astronomical Camera by Susan Kern and Don Mccarthy
    www.astrosociety.org/uitc No. 50 - Spring 2000 © 2000, Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, CA 94112. Making Your Own Astronomical Camera by Susan Kern and Don McCarthy An Education in Optics Dissect & Modify the Camera Loading the Film Turning the Camera Skyward Tracking the Sky Astronomy Camp for All Ages For More Information People are fascinated by the night sky. By patiently watching, one can observe many astronomical and atmospheric phenomena, yet the permanent recording of such phenomena usually belongs to serious amateur astronomers using moderately expensive, 35-mm cameras and to scientists using modern telescopic equipment. At the University of Arizona's Astronomy Camps, we dissect, modify, and reload disposed "One- Time Use" cameras to allow students to study engineering principles and to photograph the night sky. Elementary school students from Silverwood School in Washington state work with their modified One-Time Use cameras during Astronomy Camp. Photo courtesy of the authors. Today's disposable cameras are a marvel of technology, wonderfully suited to a variety of educational activities. Discarded plastic cameras are free from camera stores. Students from junior high through graduate school can benefit from analyzing the cameras' optics, mechanisms, electronics, light sources, manufacturing techniques, and economics. Some of these educational features were recently described by Gene Byrd and Mark Graham in their article in the Physics Teacher, "Camera and Telescope Free-for-All!" (1999, vol. 37, p. 547). Here we elaborate on the cameras' optical properties and show how to modify and reload one for astrophotography. An Education in Optics The "One-Time Use" cameras contain at least six interesting optical components.
    [Show full text]
  • Low-Cost Computational Astrophotography
    Low-cost Computational Astrophotography Joseph Yen Peter Bryan Electrical Engineering Electrical Engineering Stanford University Stanford University [email protected] [email protected] Abstract 2. Related Work When taking photographs of the night sky, long ex- Currently, most astrophotographers compensate for posure times help photographers observe many stars, the rotation of the earth by physically moving the cam- but the rotation of the earth results in long star streak era along with the earth. However, some attempts arcs about the celestial pole. An algorithm for re- have been made to remove this requirement. To accu- moving these star streaks and substituting accurately rately localize stars in streaked images, one researcher placed point-like stars is designed and implemented. has re-mapped the star streak to polar coordinates, so Images containing star streaks are transformed into that all stars will have the same point-spread function. ones with un-streaked starry skies while retaining This technique was designed for locating specific stars color and brightness information. The procedure is for the purpose of identifying specific stars, but will shown to work consistently on a 35-image dataset. be applicable for our purposes when removing star streaks [4]. Other factors besides streaking can cause quality degradation in star images, and attempts have 1. Introduction been made to correct this. These have used such tech- niques as Richardson-Lucy deblurring [2] and maxi- Astrophotography is a widespread pastime in which mally sparse optimization [1]. DSLR cameras are used to take images of objects in space. Certain factors make this a very expen- sive hobby.
    [Show full text]
  • Depth of Field in Photography
    Instructor: N. David King Page 1 DEPTH OF FIELD IN PHOTOGRAPHY Handout for Photography Students N. David King, Instructor WWWHAT IS DDDEPTH OF FFFIELD ??? Photographers generally have to deal with one of two main optical issues for any given photograph: Motion (relative to the film plane) and Depth of Field. This handout is about Depth of Field. But what is it? Depth of Field is a major compositional tool used by photographers to direct attention to specific areas of a print or, at the other extreme, to allow the viewer’s eye to travel in focus over the entire print’s surface, as it appears to do in reality. Here are two example images. Depth of Field Examples Shallow Depth of Field Deep Depth of Field using wide aperture using small aperture and close focal distance and greater focal distance Depth of Field in PhotogPhotography:raphy: Student Handout © N. DavDavidid King 2004, Rev 2010 Instructor: N. David King Page 2 SSSURPRISE !!! The first image (the garden flowers on the left) was shot IIITTT’’’S AAALL AN ILLUSION with a wide aperture and is focused on the flower closest to the viewer. The second image (on the right) was shot with a smaller aperture and is focused on a yellow flower near the rear of that group of flowers. Though it looks as if we are really increasing the area that is in focus from the first image to the second, that apparent increase is actually an optical illusion. In the second image there is still only one plane where the lens is critically focused.
    [Show full text]
  • DSLR Astrophotography They Say… Start with a Joke
    DSLR Astrophotography They say… start with a joke. DLSR Wide-field Astrophotography The Advantages It’s Relatively Inexpensive All you need is a DLSR camera …and a tripod You Don’t Need This! Nikon v.s. Canon Most DSLR astrophotographers use Canon cameras. Canon releases the details of the camera’s software. This allows the development of third party software, designed specifically for astrophotography. Nikon does not create a truly raw image A simple median blurring filter is always applied... removing many stars, as they are seen as noise. This prohibits precise image calibration. Some Nikons allow the “Mode 3” work around. Using Nikon’s Mode 3 Simply start the bulb time exposure and terminate it by turning off the camera. The camera sees this as a low-power warning and immediately saves the image without running the median blurring filter Testing For Mode 3 Availability Take a one-minute dark exposure in Mode 1. This is a raw image with “no noise reduction” selected. Take a one-minute Mode 3 dark exposure. If Mode 3 is available, that exposure will have noticeably more hot pixels and noise. For Starters… Keep It Simple Set the focus to infinity... before it’s dark Mount the camera on a sturdy tripod Use a wide angle lens (18mm is nice) Set the lens to its lowest f-stop Use the RAW image format, at the highest ISO setting Shoot 20-30 second exposures Take about five dark exposures (more on this later) …and you can get an image like this! Nikon D40X 18mm @ f/4 ISO 1600 Mode 1 4 30-Sec exposures 4 30-Sec darks After taking several Milky Way shots it may be time to get more adventurous.
    [Show full text]
  • The Trade-Off Between Image Resolution and Field of View: the Influence of Lens Selection
    The Trade-off between Image Resolution and Field of View: the Influence of Lens Selection “I want a lens that can cover the whole parking lot and I want to be able to read a license plate.” Sound familiar? As a manufacturer of wide angle lenses, Theia Technologies is frequently asked if we have a product that allows the user to do both of these things simultaneously. And the answer is ‘it depends’. It depends on several variables - the resolution you start with from the camera, how far away the subject is from the lens, and the field of view of the lens. But keeping the first two variables constant, the impact of the lens field of view becomes clear. One of the important factors to consider when designing video surveillance installations is the trade-off between lens field of view and image resolution. Image Resolution versus Field of View One important, but often neglected consideration in video surveillance systems design is the trade-off between image resolution and field of view. With any given combination of camera and lens the native resolution from the camera is spread over the entire field of view of the lens, determining pixel density and image resolution. The wider the resolution is spread, the lower the pixel density, the lower the image resolution or image detail. The images below, taken with the same camera from the same distance away, illustrate this trade-off. The widest field of view allows you to cover the widest area but does not allow you to see high detail, while the narrowest field of view permits capture of high detail at the expense of wide area coverage.
    [Show full text]
  • A Guide to Smartphone Astrophotography National Aeronautics and Space Administration
    National Aeronautics and Space Administration A Guide to Smartphone Astrophotography National Aeronautics and Space Administration A Guide to Smartphone Astrophotography A Guide to Smartphone Astrophotography Dr. Sten Odenwald NASA Space Science Education Consortium Goddard Space Flight Center Greenbelt, Maryland Cover designs and editing by Abbey Interrante Cover illustrations Front: Aurora (Elizabeth Macdonald), moon (Spencer Collins), star trails (Donald Noor), Orion nebula (Christian Harris), solar eclipse (Christopher Jones), Milky Way (Shun-Chia Yang), satellite streaks (Stanislav Kaniansky),sunspot (Michael Seeboerger-Weichselbaum),sun dogs (Billy Heather). Back: Milky Way (Gabriel Clark) Two front cover designs are provided with this book. To conserve toner, begin document printing with the second cover. This product is supported by NASA under cooperative agreement number NNH15ZDA004C. [1] Table of Contents Introduction.................................................................................................................................................... 5 How to use this book ..................................................................................................................................... 9 1.0 Light Pollution ....................................................................................................................................... 12 2.0 Cameras ................................................................................................................................................
    [Show full text]
  • Notes on View Camera Geometry∗
    Notes on View Camera Geometry∗ Robert E. Wheeler May 8, 2003 c 1997-2001 by Robert E. Wheeler, all rights reserved. ∗ 1 Contents 1 Desargues’s Theorem 4 2 The Gaussian Lens Equation 6 3 Thick lenses 8 4 Pivot Points 9 5 Determining the lens tilt 10 5.1Usingdistancesandangles...................... 10 5.2Usingbackfocus........................... 12 5.3Wheeler’srules............................ 13 5.4LensMovement............................ 14 5.5BackTilts............................... 14 6Depthoffield for parallel planes 15 6.1NearDOFlimit............................ 15 6.2FarDOFlimit............................ 17 6.3DOF.................................. 17 6.4Circlesofconfusion.......................... 18 6.5DOFandformat........................... 19 6.6TheDOFequation.......................... 19 6.7Hyperfocaldistance......................... 20 6.8Approximations............................ 21 6.9Focusgivennearandfarlimits................... 21 6.9.1 Objectdistances....................... 21 6.9.2 Imagedistances........................ 22 7Depthoffield, depth of focus 23 8Fuzzyimages 24 9Effects of diffractiononDOF 26 9.1Theory................................. 26 9.2Data.................................. 27 9.3Resolution............................... 29 9.4Formatconsiderations........................ 31 9.5Minimumaperture.......................... 32 9.6Theoreticalcurves.......................... 33 10 Depth of field for a tilted lens 35 10.1NearandfarDOFequations.................... 35 10.2 Near and far DOF equations in terms of ρ ............
    [Show full text]
  • The Rise and Fall of Astrophotography Dr
    Page2 GRIFFITH OBSERVER August The Rise and Fall of Astrophotography Dr. Joseph S.Tenn Department of Physics and Astronomy Sonoma State University Rohnert Park, California HONORABLE MENTION HUGHES GRIFFITH OBSERVER CONTEST 1987 Dr. Joe Tenn’s carefully crafted articles seem to be able to win a prize in the annual Hughes Aircraft Company Science Writing Contest any time he chooses to enter, and his students have occasionally won prizes, too. This heartens our outlook on higher education in America and provides interesting and unusual material for readers of this magazine. His last article, “Simon Newcomb, a Famous and Forgotten American Astronomer," appeared in the November, 1987, issue of the Griffith Observer, almost two years ago. It was saddled with several errors imposed by the editor, not the author, and we hope this time we have given Dr. Tenn’s most recent contribution more reliable preparation for print. His attention this time is fixed on the development of astrophotography. Onthe occasion of the January, 1987, American the first serious uses of chemical emulsions for Astronomical Society meeting in Pasadena, professional research. Less than fifty years earlier visiting astronomers were invited to tour the the first crude experiments suggested the Palomar Observatory. The five-meter telescope, possibility that astronomical information might be towering five stories above us, looked as imposing recorded photographically. as ever, although it had been in operation nearly four decades and was no longer the world's DaQUe"'9°iYPe$ largest. Astronomers were involved with photography The real surprise, to this visitor at least, was from its beginning. It was the French astronomer that the telescope is no longer used for photo- Francois Arago who made the first public graphy.
    [Show full text]
  • Astrophotography Tales of Trial & Error
    Astrophotography Tales of Trial & Error Dave & Marie Allen AVAC 13th April 2001 Contents Photos Through Camera Lens magnification Increasing 1 Star trails 2 Piggy back Photos Through the Telescope 3 Prime focus 4 Photo through the eyepiece 5 Eyepiece projection Camera Basics When the photograph is being exposed, Light directed to viewfinder the light is directed onto the film. The viewfinder is completely black. Usual photographic rules apply: Less light ! Longer exposures Higher f number ! Longer exposures Light directed to film Star Motion Stars rise and set – just like the Sun in the daytime. The motion of the stars can cause problems for astrophotography Star Motion Stars rise and set – just like the Sun in the daytime. The motion of the stars can cause problems for astrophotography Star Motion Stars rise and set – just like the Sun in the daytime. The motion of the stars can cause problems for astrophotography Star Motion Stars rise and set – just like the Sun in the daytime. The motion of the stars can cause problems for astrophotography Star Motion Stars rise and set – just like the Sun in the daytime. The motion of the stars can cause problems for astrophotography Tracking the motion of the stars during the exposure is called “guiding”. Requires a polar aligned mount and periodic corrections to keep the subject stationary relative to the camera. Done using slow motion controls – or more often with dual axis correctors. Guiding Photography Technique Guiding Required? Star trails No Piggy back Yes Prime focus Yes Photo through the
    [Show full text]
  • Tutorials: Depth of Field
    TUTORIALS: DEPTH OF FIELD Ed. Note: Information presented by Steve Fowler – 10/15/14 Camera Club Meeting Depth of field refers to the range of distance that appears acceptably sharp. It varies depending on camera type, aperture and focusing distance, although print size and viewing distance can also influence our perception of depth of field. This tutorial is designed to give a better intuitive and technical understanding for photography, and provides a depth of field calculator to show how it varies with your camera settings. The depth of field does not abruptly change from sharp to unsharp, but instead occurs as a gradual transition. In fact, everything immediately in front of or in back of the focusing distance begins to lose sharpness — even if this is not perceived by our eyes or by the resolution of the camera. CIRCLE OF CONFUSION Since there is no critical point of transition, a more rigorous term called the "circle of confusion" is used to define how much a point needs to be blurred in order to be perceived as unsharp. When the circle of confusion becomes perceptible to our eyes, this region is said to be outside the depth of field and thus no longer "acceptably sharp." The circle of confusion above has been exaggerated for clarity; in reality this would be only a tiny fraction of the camera sensor's area. When does the circle of confusion become perceptible to our eyes? An acceptably sharp circle of confusion is loosely defined as one which would go unnoticed when enlarged to a standard 8x10 inch print, and observed from a standard viewing distance of about 1 foot.
    [Show full text]